Abstract: Based on air pollutant monitoring data from 2013 to 2017 and the LiDAR data from December of 2015 to February of 2017 observed at Zhenhai (a coastal station) and Fenghua (an inland station) in Ningbo,the characteristics of air quality at the two stations were comparatively analyzed,and the aerosol sources and difference of atmospheric self-purification capacity at the two stations were evaluated using the reanalysis data from National Centre for Environment Prediction (NCEP) Global Data Assimilation System (GDAS) and ERA-Interim high-resolution dataset.The results showed that moderate and heavier air pollution occur mostly in winter in the coastal and inland areas of Ningbo,with PM_2.5 as the primary pollutants commonly.The NO₂ concentrations in Zhenhai area are significantly higher than that in Fenghua,and concentrations of PM_2.5 and PM₁₀ between the two areas are close to each other.In winter,an aerosol layer below 3 km with large extinction coefficient are observed at both stations,and the average of extinction coefficient below 3 km at Zhenhai station is about 40% larger than that observed at Fenghua station.When moderate and heavier pollution occur at both stations,aerosols are mainly originated from the northwestern inland region of Ningbo,reaching 90% for Zhenhai and 63% for Fenghua,respectively.The rest aerosols in Zhenhai are mainly related to the short-range transport by easterly flows at low levels,and that in Fenghua are primarily due to the short-range transport from the southwestern region of Zhejiang province.The northern coastal areas in Zhejiang province is usually dominated by northeasterly and northwesterly winds when air quality in Ningbo region reaches grades of excellence,moderate,and heavier pollution during winter,with mean wind speed of the former higher than the latter. The ratio of atmospheric self-cleaning capacity between air quality grades of excellence and moderate and heavier pollution decreases from the northwest to the southeast in Zhejiang province,with the value about 1.5 times Ningbo area.The difference of atmospheric self-purification capacity under different air quality grades can be used as a reference for forecasting the occurrence,development and dissipation of air pollution.

Key words: Profile of extinction coefficient, Backward trajectory analysis, Atmospheric self-purification capacity, Air quality grade, Primary pollutant